1. Field of the Invention
The present invention relates to an apparatus and a method for evaluating antifog properties of window glasses, mirrors, or various lenses, for example.
2. Description of the Related Art
Evaluation on the antifog properties, which indicate tolerance to fogging, of window glasses, mirrors, or various lenses, for example, has been conducted in conventional techniques mainly by sensory tests by means of visual observation. Examples of such a sensory test include a breath antifog property test, a steam antifog property test, and a low-temperature antifog property test. In the breath antifog property test, a sample is breathed on to visually check the state of fogging in the sample. The antifog property of the sample is evaluated on a scale of about three to four levels on the basis of the presence or absence of fogging, the degree of blur in sight seen via transmission through the sample or reflection by the sample, etc. In the steam antifog property test, a sample is placed above hot water in a thermostatic bath to visually check the deposition state of water droplets on the sample. The antifog property of the sample is evaluated on a scale of about three to four levels on the basis of the presence or absence of the water droplets, the size of the water droplets, etc. In the low-temperature antifog property test, the presence or absence of fogging is evaluated on a scale of two levels when a sample cooled in a refrigerator or a freezer (for example, −20 to 5° C.) is brought back to a normal environment (for example, 20° C. and 65% RH). In these conventional sensory tests, however, evaluation greatly varies from person to person, and thus lacks in stability. Therefore, it has been difficult to evaluate the antifog property quantitatively and objectively.
In view of this, a method for objectively evaluating an antifog property by projecting an image of an object drawing a plurality of vertical lines or a grid on a sample in the above low-temperature antifog property test and measuring a condensation area (fogging area) on a surface of the sample on the basis of such vertical lines or grid, for example, has been proposed (see Patent Literature 1, for example). Also, a method for calculating an antifog property evaluation index on the basis of the degree of scattering of spot light projected on a sample to quantitatively and objectively evaluate the antifog property of the sample on the basis of the antifog property evaluation index has been proposed by the present applicants (see Patent Literature 2, for example).    Patent Literature 1: Japanese Patent No. 3564085    Patent Literature 2: Japanese Patent No. 5015183